Rhesus Factor
When you have your first antenatal appointment with your midwife
or doctor, you will be given a form for your first set of antenatal
blood tests. As well as checking your white cell count, iron and
rubella immunity, these blood tests will also tell your midwife
whether your blood type is Rhesus negative or Rhesus positive.
It's important to know whether you are Rhesus negative or Rhesus
positive, as if you are Rhesus negative and the father of your baby
is Rhesus positive, there is a chance that your baby will inherit
his or her father's positive blood.
This can be a problem if the baby's blood mixes with yours at
any stage during the pregnancy. If this happens, your body may view
the Rhesus positive blood as foreign and create antibodies to fight
it, much in the same way as our bodies create antibodies to fight
off colds and flu. This is known as Rhesus disease, and can make
your baby sick. The effects of Rhesus disease on your baby can
range from jaundice after birth in mild cases, right through to
stillbirth in more severe cases.
If you are Rhesus positive you have nothing to worry about, even
if your baby's father is Rhesus negative and your baby inherits his
blood type it will not pose a problem. If you are Rhesus negative,
your midwife or doctor will discuss what you need to do to ensure
you don't develop Rhesus disease.
If you are Rhesus negative and your baby's father is Rhesus
positive, or his blood type is unknown, your midwife or doctor will
probably recommend:
• That you contact him/her urgently if you have any
spotting and/or bleeding after the start of the second trimester
(in the first trimester bleeding is usually from the mother, not
the baby, but you should always contact your midwife or doctor for
advice).
• That if you do have any bleeding in the second or third
trimester, you should be offered an injection of Anti-D. Anti-D
destroys any Rhesus positive blood cells that may have passed into
your bloodstream, and prevents your body making antibodies to fight
them. In some countries Anti-D is given routinely during pregnancy
as a preventative measure, but this is not current practice in New
Zealand. You have up to 72 hours after the onset of bleeding to
have the Anti-D injection.
• That if you elect to have an amniocentesis, CVS or External Cephalic
Version during pregnancy you should be given an Anti-D injection as
a preventative.
• That if you are involved in an accident or fall or any
other situation where there may have been impact to the baby you
should be given an Anti-D injection as a preventative.
• That after your baby is born a sample of the cord blood
will be taken and tested to identify whether your baby has Rhesus
negative or Rhesus positive blood. If your baby is Rhesus positive
you will be given an injection of Anti-D to destroy any Rhesus
positive blood cells that have passed into your blood stream during
delivery. If your baby is Rhesus negative this is not
necessary.
You should also have an injection of Anti-D after a miscarriage or abortion.
If you have developed Rhesus disease as the result of your
baby's blood mixing with yours during pregnancy, you will require
specialist care during subsequent pregnancies to ensure that your
body is not making antibodies to harm your baby. If your body does
begin making antibodies that attack your baby your specialist will
go over your options which include an in-utero blood transfusion
for your baby, and/or a blood transfusion for your baby in the
first few days of life.
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